posted by Carl .
What is the area of a quadrilateral with vertices at (1, 1), (4, 1), (7, 5) and (4, 5)?
Did you notice that points (1,1) and (4,1) form a horizontal line, as do (7,5) and (4,5) ??
So if we use the first two points to form the base, the base has length 3, and the height between the two parallel lines is 4
So the area is 3x4 or 12 square units.
This was a lucky case.